One method of copper brazing is in a furnace, for example, in a batch-type or continuous conveyor-type furnace. In both types of furnaces, heating is usually by hydrocarbon fueled burners or electrical resistance. The parts are fixtured and assembled with filler metals pre-placed near or in the joint. One example of copper brazing in a furnace is illustrated in FIG. 1(a) and FIG. 1(b). The articles to be joined by the brazing process may be stainless steel tube 102 and threaded fitting 104 with an open interior. Threaded fitting 104 is furnace brazed to the tube around hole 105 formed along the length of the tube. Prior to the furnace brazing process, one or more tack welds 106 are made between tube 102 and fitting 104 to hold a copper alloy filler 108 in place between the tube and fitting as illustrated in FIG. 1(a). Entire tube 102, with the tack welded threaded fitting 104, as shown in FIG. 1(a), is passed through furnace 110 having an internal temperature sufficient to melt the copper alloy filler for the brazing process that forms the brazed joint between the tube and fitting as illustrated in FIG. 1(b). Subsequent to exit from the furnace, an end fitting, such as end cap 112 (shown in detail in FIG. 1(c)) can be brazed to end 102a of tube 102, for example, by electric induction brazing using a silver alloy filler 114. As shown in FIG. 1(d), end 102a of tube 102 is top inserted into rectangular brazing box 116. End cap fitting 112 is seated on the end of linear driver 120 with silver alloy filler 114 seated on top of the end cap fitting. The end of linear driver 120 is initially positioned at the bottom of the brazing box as indicated in solid lines in FIG. 1(d). Linear driver 120 raises the end cap fitting, with the silver alloy filler sitting on top of the end cap fitting, to mate with end 102a of tube 102 as indicated in dashed lines in FIG. 1(d). Establishing a nitrogen atmosphere in the brazing box from a supply of nitrogen and supplying alternating current to ring induction coil 118 in the brazing box, induction brazes the end cap fitting 112 to end 102a of tube 102. One side of the brazing box can be formed from a hinged translucent panel so that an operator can observe the brazing process, and to facilitate placement of the end cap fitting and silver alloy filler on the end of linear driver 120.
Disadvantages of furnace copper brazing include: potential for distortion due to heating of the entire part; annealing in undesirable regions of the part: high rate of gas consumption; high operating cost; batching of parts in a batch-type furnace without one piece flow; and complicated fixturing.
Another method of copper brazing is by torch, for example, with a handheld oxyfuel gas torch using various fuels. Disadvantages of manual torch copper brazing include: manual fixturing; addition of too little or too much braze alloy; insufficient addition of flux; and quality inconsistencies between successive parts.
Included in the objectives of the present invention is to provide a copper brazing process by electric induction that: results in high tensile strength brazed joints; uses a low cost and corrosion resistance copper alloy filler; is fluxless; results in clean parts; localizes application of heat, which results in less distortion of the part; is adaptable to cellular environment manufacturing; is a one piece flow process with no product batching required; and uses a low amount of cover gas.